This invention relates to network video delivery technology and particularly to the video delivery device, the video receiver and the key frame delivery method for achieving the trick play such as fast-forward.
In recent years, with the progress in network technology represented by the Internet, Video on demand (VOD) delivery on the network of video contents such as motion pictures has spread. In the VOD delivery, in addition to the conventional streaming delivery from a video delivery server to a personal computer (PC), VOD delivery system taking set top box (STB) connected to a television set, or a television set containing a function of STB as a client has been starting.
In these VOD delivery systems, there has been a strong demand even in the case of streaming delivery on the network toward the trick plays such as fast-forward and rewinding, which have been widely achieved in the conventional video devices. In order to meet this demand, it is necessary to generate a video stream taking the trick play into consideration in the video delivery server and deliver the same to the client such as STB.
In order to achieve the trick play, a video server device described in Japanese Patent Application Laid-Open Publication No. H10-032809, discloses the technology of generating a video stream including only a frame in which intra-frame encoding is performed (a key frame) from the compression-encoded video data and transmitting the same at an optional double speed.
In the conventional method, it is supposed that key frames are included at fixed intervals in the video contents in order to achieve reproduction at an optional double speed, the interval for reading the key frame from the video contents and delivering the same is calculated as a fixed value, and the key frames are delivered according to the internals.
The intervals of key frames included in the video contents are, however, not always fixed, and especially in the video contents of the variable bit rate (VBR), the insertion intervals of key frames often vary largely with the intensity of motion of an animation to improve the compression efficiency. Even in the case of video contents of the constant bit rate (CBR), there are some video contents where in some algorithm of encoding, the insertion interval of key frames varies, so that the key frames are often lost due to an error or the like in editing and transmitting the encoded video contents, and the key frames do not appear at fixed intervals.
In the case of applying the method disclosed in Japanese Patent Application Laid-Open Publication No. H10-032809 to the video contents where the key frames are not included at fixed intervals, in a part with thin intervals of key frames, the reproduction time of the video contents is accelerated, and in a part with dense intervals of key frames, the reproduction time of the video contents is decelerated, resulting in the possibility of causing a lag between the delivery time of key frames to be transmitted and the reproduction time. On the other hand, in the case of applying the method to the video contents lacking key frames, when the trick play is continued for a long time, a lag between the delivery time of the key frame and the reproduction time is accumulated, resulting in the possibility that the non-coincidence between the delivery time and the reproduction time of contents in the trick play becomes remarkable.